Inkjet printheads are devices for printing an image on a printing medium by ejecting droplets of ink onto a desired region of the printing medium. Inkjet printheads can be classified into two different types depending on the mechanism of ejecting ink droplets: (1) a thermal inkjet printhead, in which ink is heated to form ink bubbles and the expansive force of the bubbles causes ink droplets to be ejected; and (2) a piezoelectric inkjet printhead, in which a piezoelectric crystal is deformed and the pressure due to the deformation causes ink droplets to be ejected.
The mechanism of ejecting ink droplets of the thermal inkjet printhead will be described in more detail. When current in the form of pulse wave is supplied to a heater formed of a heating resistor, ink surrounding the heater is instantly heated to about 300° C. due to the heat generated by the heater. Accordingly, ink boils to generate bubbles, and the bubbles expand to apply pressure to ink filled in an ink chamber. Thus, ink in the vicinity of a nozzle is ejected through the nozzle in the form of droplets.
The thermal inkjet printhead can have a structure in which a chamber layer and a nozzle layer are sequentially stacked on a substrate on which a plurality of material layers are formed. In this regard, a plurality of ink chambers, which are filled with ink to be ejected, are formed in the chamber layer, and a plurality of nozzles through which ink is ejected are formed in the nozzle layer. Also, the substrate may have an ink feed hole for supplying ink to the ink chambers.